Vaillant ecoTEC boilers show a fault code on the display when something goes wrong. Here's what the most common F codes mean, the safe checks you can do yourself, and when to book a Gas Safe registered engineer.
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Vaillant is one of the most widely fitted boiler brands in UK homes, and the ecoTEC range (ecoTEC plus, ecoTEC pro and ecoTEC exclusive) is known for being reliable. But like any condensing boiler, it can throw up a fault from time to time. The good news is that Vaillant boilers tell you exactly what's wrong: a code beginning with F appears on the digital display, each one pointing to a specific problem.
This guide is a hub for the most common Vaillant faults. Some have a homeowner-safe fix you can try in a couple of minutes; others are a clear sign to call a Gas Safe registered engineer. We'll always tell you which is which.
Safety first. Your boiler burns gas, so there are strict limits on what you should touch. Bleeding radiators, topping up pressure via the filling loop, resetting once from the front panel and checking the power supply are all fine. Anything involving the gas valve, internal pipework, the flue, the sealed heating circuit or removing the casing is a job for a Gas Safe registered engineer only — never DIY. If you smell gas, call the National Gas Emergency line on 0800 111 999 immediately.
Use the table below to find your code, see what it usually means, and jump to a detailed guide. The "Safe to try?" column tells you whether there's a homeowner check worth attempting first.
| Code | What it usually means | Safe to try? | Detailed guide |
|---|---|---|---|
| F22 | Low water pressure / dry-fire protection — the boiler has too little water in the system | Yes — top up pressure | F22 guide |
| F28 | Ignition failure on start-up — the boiler won't light | Limited — check gas & reset | F28 guide |
| F29 | Flame lost during operation — the boiler lights then cuts out | Limited — check gas & reset | F29 guide |
| F75 | Pump or pressure-sensor fault — no pressure change detected when the pump runs | No — engineer required | F75 guide |
Two other common Vaillant problems don't always show a single code, so we've covered them separately: a boiler giving heating but no hot water, and our general guide to Vaillant boiler repair covering costs, parts and what to expect.
F22 is the fault most homeowners can fix themselves. Vaillant ecoTEC boilers need the heating system to hold a minimum amount of water; if the pressure drops too low, the boiler shuts down to protect itself. Check the pressure gauge on the front of the boiler — when cold it should read roughly 1 to 1.5 bar, rising towards 2 bar when the system is hot.
If it's reading below 1 bar, you can usually top it up using the filling loop (the small braided silver hose underneath the boiler). Open both valves slowly until the gauge reaches about 1.2 bar, then close them and reset the boiler. Our full F22 guide walks through it step by step. If the pressure keeps dropping after you top up, there's a leak somewhere in the system — that needs an engineer.
F28 means the boiler failed to ignite when it tried to fire up; F29 means it lit but then lost the flame. Both can be triggered by something simple, such as a temporary gas-supply interruption, so it's worth a couple of basic checks: make sure other gas appliances (your hob or oven) are working, that your gas supply hasn't been cut off, and that the boiler's condensate pipe isn't frozen in cold weather. After that, you can press the reset button on the front panel once.
If the code returns straight away, stop there. Persistent F28 or F29 faults usually point to the gas valve, ignition electrodes, flue or condensate system — none of which a homeowner should touch. Book a Gas Safe registered engineer. See the F28 guide and F29 guide for the full picture.
The one-reset rule. It's fine to reset a Vaillant boiler once from the front panel. If the same fault comes back, don't keep resetting — repeatedly cycling a boiler that's locked out can mask a genuine fault and, in the case of ignition faults, isn't safe. One reset, then call an engineer.
F75 appears when the boiler can't detect a change in water pressure when the pump starts. It usually points to a faulty pump, a stuck pressure sensor or trapped air in the system. There's no safe homeowner fix for this one — it involves the sealed heating circuit and internal components — so it's an engineer job. Our F75 guide explains the likely causes and typical repair costs.
Before calling anyone out, these homeowner-safe checks resolve a surprising number of "faults":
Call a professional if: a fault code returns after one reset; the pressure won't hold after topping up (a leak); you have ignition faults (F28/F29) that don't clear; you see F75 or any pump/sensor code; or you ever smell gas or see sooting around the boiler. By law, only an engineer on the Gas Safe Register may work on the gas side of your boiler. You can check any engineer's registration on that site before they start.
Most boiler cover and home-emergency policies will send a Gas Safe engineer to diagnose and repair faults like these, often with parts and labour included up to a claim limit. Cover can make sense if an out-of-warranty repair would otherwise land you with an unexpected bill — though it isn't right for everyone. We weigh it up in is boiler cover worth it? and explain the basics in what is boiler cover?. You can also compare boiler cover from our selected panel of providers to see what's included.
See cover options from our selected panel of UK providers, with parts and labour from Gas Safe registered engineers. Information, not advice — we show a selected panel, not the whole market.
Compare boiler coverOn most ecoTEC plus and pro models it's a clearly marked reset button on the front control panel; on some it's combined with the dial. Press it once. If the fault returns, don't keep resetting — book a Gas Safe registered engineer.
Roughly 1 to 1.5 bar when the system is cold, rising towards about 2 bar when it's hot. If it's below 1 bar you can top it up via the filling loop. If it keeps dropping, you likely have a leak that needs an engineer.
Only the basic checks — confirm your gas supply is on, other gas appliances work, the condensate pipe isn't frozen, then reset once. Ignition and flame faults usually involve the gas valve, electrodes or flue, which only a Gas Safe registered engineer should touch.
Most lock-outs are the boiler protecting itself and aren't an immediate danger. But if you smell gas, see soot marks, or feel unwell with symptoms that ease when you leave the house, treat it as an emergency: turn the boiler off and call the National Gas Emergency line on 0800 111 999.
This article is general information, not professional or financial advice. Always follow your boiler's manual and use a Gas Safe registered engineer for any gas work. Boiler Cover UK is a comparison site and may earn commission; we show a selected panel of providers, not the whole market.